In manufacturing, for example, a semiconductor component or a flat panel display (FPD), a substrate liquid processing apparatus is employed to process a substrate such as a semiconductor wafer or a liquid-crystal substrate with a processing liquid such as a cleaning liquid or an etching liquid.
In a conventional substrate liquid processing apparatus, a circulation flow path is connected to a processing liquid storage tank that stores a processing liquid, and a pump and a heater are installed in the middle of the circulation flow path. The pump is driven to allow the processing liquid to flow through the circulation flow path, and the heater heats the processing liquid to a predetermined temperature such that the heated processing liquid returns to the processing liquid storage tank. Then, a substrate is immersed into the processing liquid storage tank that stores the processing liquid at the predetermined temperature, thereby performing a liquid processing on the substrate.
In this substrate liquid processing apparatus, in order to clean a sensor unit of a concentration sensor for measuring the concentration of the processing liquid, deionized water is supplied into the flow path through which the processing liquid flows (circulation flow path) (see, e.g., Japanese Patent Laid-Open Publication No. 09-199468).